PSI - Issue 72

Oleksandr Chapiuk et al. / Procedia Structural Integrity 72 (2025) 308–314

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In the P- 2 specimens, a value of δu =0.2 mm was reached at an average rod stress of σs0m =248.8 MPa. Slippage started at a stress of σs=74.6 MPa, also with a displacement of δ=0.001 mm. Good homogeneity was noted in the P-3 specimens, where a value of δu =0.2 mm was found at an average rod stress of σs0m =398.0 MPa. Slippage began at a stress of σs=248.6 MPa, resulting in a displacement of δ=0.001 mm. Increasing the length of the anchorage raised the stress at which slippage starts and the stress corresponding to the adhesion limit state (Fig. 2).

σ s , МPа

500

3

400

300

2

200

100

1

δ , mm

0

0

0,05 0,10 0,15 0,20 0,25

Fig. 2. Variation of rod slippage δ depending on the stress σ s : 1 – P-1; 2 – P-2; 3 – P-3

It is important to note that all the prisms fragilely collapsed under increased load after reaching a displacement of δ u = 0.2 mm, with fractures occurring along the rods (see Fig. 3a, Fig. 3b, Fig. 3c). When the anchoring length was smaller, cracks began to form at the contact point with the bottom plate of the press, whereas for a larger anchoring length, cracks initiated from the free end of the prisms. Therefore, it can be inferred that a slip value of δ = 0.2 mm at the free end of the rod in concrete can serve as a criterion for determining the limit state of adhesion of sickle-shaped reinforcement to concrete.

Fig. 3. (a) fracture pattern of sample P-1; (b) fracture pattern of sample P-2; (c) fracture pattern of sample P-3

Based on the test results, the average maximum tangential adhesion stresses τ um were calculated for each group of samples, assuming they are constant along the length of the rod, following the formula.   an s m s um dl A    / 0  , (1) The analysis of experimental studies indicates that the stresses in the rods, which occur in the limiting state of adhesion at δu=0.2 mm, depend linearly on the anchoring lengt h and can be determined using formula (2)